Method and system for image background suppression using neutral adjustment of color channels

Abstract

Printing systems and methods are presented for image background and neutral adjustment of luminance-chrominance pixel values corresponding to a scanned image, in which white and black pixels are identified which have luminance values close to whitepoint and blackpoint values for the image, and which have chrominance values close to the chrominance neutral point. The chrominance values of these identified white and black pixels are selectively reduced based at least partially on proximity to the chrominance neutral point and chrominance of one or more neighboring pixels.

1. A method of image background adjustment, the method comprising:
 receiving luminance-chrominance pixel values, a whitepoint value, and a blackpoint value which correspond to an image; 
 using a hardware processing element identifying white pixels having luminance values within a white offset value of the whitepoint value and having chrominance values within a non-zero white chrominance threshold value of a chrominance neutral point; 
 using the hardware processing element identifying black pixels having luminance values within a black offset value of the blackpoint value and having chrominance values within a non-zero black chrominance threshold value of the chrominance neutral point; and 
 using the hardware processing element adjusting pixels by selectively reducing the chrominance values of the identified white and black pixels based at least partially on proximity to the chrominance neutral point and chrominance of at least one neighboring pixel. 
 
     
     
       2. The method of  claim 1 , wherein the white chrominance threshold value is greater than the black chrominance threshold value. 
     
     
       3. The method of  claim 1 , wherein selectively reducing the chrominance values of the identified white and black pixels comprises:
 for identified white and black pixels with chrominance values within a chrominance adjustment threshold of the chrominance neutral point, adjusting the chrominance values to the chrominance neutral point using the hardware processing element, the chrominance adjustment threshold being less than the white chrominance threshold value and less than the black chrominance threshold value; 
 for remaining identified white pixels with chrominance values not within the chrominance adjustment threshold of the chrominance neutral point using the hardware processing element, selectively reducing the chrominance values of the remaining identified white pixels for which at least one neighboring pixel is an identified white pixel; and 
 for remaining identified black pixels with chrominance values not within the chrominance adjustment threshold of the chrominance neutral point, selectively reducing the chrominance values of the remaining identified black pixels for which at least one neighboring pixel is an identified black pixel using the hardware processing element. 
 
     
     
       4. The method of  claim 3 :
 wherein selectively reducing the chrominance values of the remaining identified white pixels for which at least one neighboring pixel is an identified white pixel comprises: 
 for each chrominance axis, computing an average deviation from the neutral point chrominance neutral point for identified white neighboring pixels and the current white pixel using the hardware processing element, and 
 selectively adjusting the individual chrominance values by an amount equal to either the chrominance adjustment threshold or the average deviation from the chrominance neutral point for identified white neighboring pixels and current white pixel using the hardware processing element; and 
 wherein selectively reducing the chrominance values of the remaining identified black pixels for which at least one neighboring pixel is an identified black pixel comprises: 
 for each chrominance axis, computing an average deviation from the chrominance neutral point for identified black neighboring pixels and the current black pixel using the hardware processing element, and 
 selectively adjusting the individual chrominance values by an amount equal to either the chrominance adjustment threshold or the average deviation from the neutral point for identified black neighboring pixels and current pixel using the hardware processing element. 
 
     
     
       5. The method of  claim 4 , comprising selectively further adjusting chrominance values of at least one of the identified white and black pixels using the hardware processing element based on adjusted chrominance values of neighboring pixels. 
     
     
       6. The method of  claim 3 , comprising selectively further adjusting chrominance values of at least one of the identified white and black pixels using the hardware processing element based on adjusted chrominance values of neighboring pixels. 
     
     
       7. The method of  claim 1 , comprising selectively further adjusting chrominance values of at least one of the identified white and black pixels using the hardware processing element based on adjusted chrominance values of neighboring pixels. 
     
     
       8. The method of  claim 7 , wherein further adjusting chrominance values comprises adjusting the chrominance values to the chrominance neutral point using the hardware processing element if the adjusted chrominance values of all the neighboring pixels are at the chrominance neutral point. 
     
     
       9. The method of  claim 7 , further comprising selectively further adjusting chrominance values of at least one of the identified white and black pixels to the chrominance neutral point using the hardware processing element if the adjusted chrominance values are within one of the chrominance neutral point. 
     
     
       10. The method of  claim 1 , further comprising selectively further adjusting chrominance values of at least one of the identified white and black pixels to the chrominance neutral point using the hardware processing element if the adjusted chrominance values are within one of the chrominance neutral point. 
     
     
       11. The method of  claim 1 , further comprising storing adjusted pixel values corresponding to the image in a memory using the hardware processing element. 
     
     
       12. The method of  claim 1 , further comprising:
 scanning an original document to produce a red-green-blue color pixel representation of an original image; and 
 converting values of red-green-blue pixels of the red-green-blue color pixel representation into corresponding luminance-chrominance pixel values using the hardware processing clement. 
 
     
     
       13. The method of  claim 1 , further comprising identifying non-white and non-black pixels having chrominance values within a narrow chrominance threshold value of the chrominance neutral point using the hardware processing element; and selectively reducing the chrominance values of the identified non-white and non-black pixels using the hardware processing element based at least partially on chrominance of at least two neighboring pixels if at least two neighboring pixels have chrominance values within the narrow chrominance threshold value of the chrominance neutral point and have luminance values within a narrow luminance threshold value of the current pixel luminance value. 
     
     
       14. A document processing system, comprising:
 a scanning component operative to produce a red-green-blue color pixel representation of an original image; 
 a red-green-blue color space to luminance-chrominance color space converter operative to convert values of red-green-blue pixels into corresponding luminance-chrominance pixel values; 
 a white and black pixel identification component operative to identify white pixels having luminance values within a white offset value of a whitepoint value associated with the image and having chrominance values within a non-zero white chrominance threshold value of a chrominance neutral point, and to identify black pixels having luminance values within a black offset value of a blackpoint value associated with the image and having chrominance values within a non-zero black chrominance threshold value of the chrominance neutral point; 
 a chrominance value adjustment component operative to selectively reduce chrominance values of the identified white and black pixels based at least partially on proximity to the chrominance neutral point and chrominance of at least one neighboring pixel; and 
 a memory for storing original and adjusted pixel values corresponding to the image. 
 
     
     
       15. The document processing system of  claim 14 , wherein the white chrominance threshold value is greater than the black chrominance threshold value. 
     
     
       16. The document processing system of  claim 14 , wherein the chrominance value adjustment component is operative to selectively reduce the chrominance values of the identified white and black pixels with chrominance values within a chrominance adjustment threshold of the chrominance neutral point to the chrominance neutral point; to selectively reduce the chrominance values of remaining identified white pixels for which at least one neighboring pixel is an identified white pixel for remaining identified white pixels with chrominance values not within the chrominance adjustment threshold of the chrominance neutral point; and to selectively reducing the chrominance values of remaining identified black pixels for which at least one neighboring pixel is an identified black pixel for remaining identified black pixels with chrominance values not within the chrominance adjustment threshold of the chrominance neutral point; where the chrominance adjustment threshold is less than the white chrominance threshold value and less than the black chrominance threshold value. 
     
     
       17. The document processing system of  claim 16 , wherein the chrominance value adjustment component is operative to selectively reduce the chrominance values of the remaining identified white pixels for which at least one neighboring pixel is an identified white pixel by computing average deviations from the chrominance neutral point for identified white neighboring pixels and current white pixel, and selectively adjusting the individual chrominance values by an amount equal to either the chrominance adjustment threshold or the average deviation from the neutral point for identified white neighboring pixels and current pixel; and wherein the chrominance value adjustment component is operative to selectively reduce the chrominance values of the remaining identified black pixels for which at least one neighboring pixel is an identified black pixel by computing an average deviation from the chrominance neutral point for identified black neighboring pixels, and by selectively adjusting the individual chrominance values by an amount equal to either the chrominance adjustment threshold or the average deviation from the neutral point chrominance neutral point for identified black neighboring pixels and current pixel. 
     
     
       18. The document processing system of  claim 17 , wherein the chrominance value adjustment component is operative to selectively further adjust chrominance values of at least one of the identified white and black pixels based on adjusted chrominance values of neighboring pixels. 
     
     
       19. The document processing system of  claim 16 , wherein the chrominance value adjustment component is operative to selectively further adjust chrominance values of at least one of the identified white and black pixels based on adjusted chrominance values of neighboring pixels. 
     
     
       20. The document processing system of  claim 14 , wherein the chrominance value adjustment component is operative to selectively further adjust chrominance values of at least one of the identified white and black pixels based on adjusted chrominance values of neighboring pixels. 
     
     
       21. The document processing system of  claim 20 , wherein the chrominance value adjustment component  160 ) is operative to further adjust chrominance values by adjusting the chrominance values to the chrominance neutral point if the adjusted chrominance values of all the neighboring pixels are at the chrominance neutral point. 
     
     
       22. The document processing system of  claim 14 , wherein the chrominance value adjustment component  160 ) is operative to further identify non-white and non- black pixels having chrominance values within a narrow chrominance threshold value of the chrominance neutral point, and to selectively reduce the chrominance values of the identified non-white and non-black pixels based at least partially on chrominance of at least two neighboring pixels if at least two neighboring pixels have chrominance values within the narrow chrominance threshold value of the chrominance neutral point and have luminance values within a narrow luminance threshold value of the current pixel luminance value.